Variable capacitor with linear impedance and high voltage breakdown

ABSTRACT

A variable capacitor includes an enclosure having first and second conductive collars separated by an intermediate electrically insulating element. A movable capacitor plate assembly is electrically coupled to the first conductive collar, and a fixed capacitor plate assembly is electrically coupled to the second conductive collar. An actuator extends into the enclosure for advancing and retracting the movable capacitor plate assembly relative to the fixed capacitor plate assembly. A hermetically sealed volume within the enclosure maintains a vacuum or a liquid serving as a dielectric between a capacitor plate of the movable capacitor plate assembly and a capacitor plate of the fixed capacitor plate assembly. At least one capacitor plate comprises a coiled cylindrical plate having a having a greater height at a center portion of the capacitor plate coil and a lower height at an outer portion of the capacitor plate coil.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to concurrently-filed U.S. Pat. Application Serial No. 17/739,595, filed in the name of Tigran Poghosyan, Anthony Oliveti, Gabe Calebotta, and Kirkwood Rough, and entitled “DIELECTRIC FLUID VARIABLE CAPACITOR,” which application is hereby incorporated by reference herein for all purposes, including right of priority in the United States and all foreign jurisdictions.

BACKGROUND

Variable capacitors are used in a variety of applications, particularly those involving high frequency, high power signals. Variable capacitors may be utilized, for example, in oscillation circuits for high-power radio transmission, high-frequency power supplies for semiconductor manufacturing equipment, and impedance matching networks in which the impedance of a time-dependent, high-frequency load is to be matched with that of a generator.

A capacitor consists essentially of two spaced-apart capacitor plates with an insulator or dielectric material disposed between the capacitor plates. As used herein, the terms “dielectric,” “dielectric material” and “dielectric medium” are interchangeably used to refer to a material (i.e., solid, liquid, or gas) which is polarizable in the presence of an electric field, typically expressed in terms of the material’s electrical susceptibility x.

In a vacuum variable capacitor, the two capacitor plates are maintained in a high vacuum, (e.g., 10⁻⁶ Torr or less) which serves as the capacitor’s dielectric, having a susceptibility x ≈ 0. In some vacuum variable capacitors, the capacitor plates may be configured as a plurality of interdigitated, concentric cylindrical coil plates, and the variability of capacitance may be achieved through physically adjusting the length of overlapping in the interdigitation.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detailed description when read with the accompanying figures, wherein:

FIG. 1 is a side external view of a vacuum variable capacitor according to one or more examples;

FIG. 2 is a cut-away perspective view of the vacuum variable capacitor of FIG. 1 ;

FIG. 3 is a side cross-sectional view of the vacuum variable capacitor of FIG. 1 with capacitor plates in a first positional relationship;

FIG. 4 is a side cross-sectional view of the vacuum variable capacitor of FIG. 1 with capacitor plates in a second positional relationship;

FIG. 5 is an exploded perspective view of stationary and movable capacitor plate assemblies in the example of FIG. 1 ;

FIG. 6 is side cross-sectional view of a vacuum variable capacitor according to another example with capacitor plates in a first positional relationship;

FIG. 7 is a side cross-sectional view of the vacuum variable capacitor from the example of FIG. 6 with the capacitor plates in a second positional relationship;

FIG. 8 is an exploded perspective view of stationary and movable capacitor plate assemblies in the example of FIG. 6 ;

FIG. 9 is side cross-sectional view of a vacuum variable capacitor according to another example with capacitor plates in a first positional relationship;

FIG. 10 is a side cross-sectional view of the vacuum variable capacitor from the example of FIG. 9 with the capacitor plates in a second positional relationship;

FIG. 11 is an exploded perspective view of stationary and movable capacitor plate assemblies in the example of FIG. 10 ;

FIG. 12 is side cross-sectional view of a vacuum variable capacitor according to another example with capacitor plates in a first positional relationship;

FIG. 13 is a side cross-sectional view of the vacuum variable capacitor from the example of FIG. 9 with the capacitor plates in a second positional relationship;

FIG. 14 is an exploded perspective view of stationary and movable capacitor plate assemblies in the example of FIG. 10 ;

FIG. 15 is a plot of impedance versus capacitor plate position for a variable capacitor having a pair of cylindrical, interdigitated spiral capacitor plates;

FIG. 16 is a plot of impedance versus capacitor plate position for variable capacitors according to the examples of FIGS. 1-14 ;

FIG. 17 is a plot of impedance versus capacitor plate position for a variable capacitor according to the example of FIGS. 15-17 ; and

FIG. 18 is a schematic representation of a matching network including variable capacitors according to one or more examples.

It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion or illustration.

DETAILED DESCRIPTION

Illustrative examples of the subject matter claimed below are disclosed. In the interest of clarity, not all features of an actual implementation are described for every example in this specification. It will be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions may be made to achieve the developers’ specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort, even if complex and time-consuming, would be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

The expressions such as “include” and “may include” which may be used in the present disclosure denote the presence of the disclosed functions, operations, and constituent elements, and do not limit the presence of one or more additional functions, operations, and constituent elements. In the present disclosure, terms such as “include” and/or “have”, may be construed to denote a certain characteristic, number, operation, constituent element, component or a combination thereof, but should not be construed to exclude the existence of or a possibility of the addition of one or more other characteristics, numbers, operations, constituent elements, components or combinations thereof.

As used herein, the article “a” is intended to have its ordinary meaning in the patent arts, namely “one or more.” Herein, the term “about” when applied to a value generally means within the tolerance range of the equipment used to produce the value, or in some examples, means plus or minus 10%, or plus or minus 5%, or plus or minus 1%, unless otherwise expressly specified. Further, herein the term “substantially” as used herein means a majority, or almost all, or all, or an amount with a range of about 51% to about 100%, for example. Moreover, examples herein are intended to be illustrative only and are presented for discussion purposes and not by way of limitation.

As used herein, to “provide” an item means to have possession of and/or control over the item. This may include, for example, forming (or assembling) some or all of the item from its constituent materials and/or, obtaining possession of and/or control over an already-formed item.

Unless otherwise defined, all terms including technical and/or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present disclosure pertains. In addition, unless otherwise defined, all terms defined in generally used dictionaries may not be overly interpreted.

The subject matter described herein is directed to examples of vacuum variable capacitors as well as vacuum variable capacitors incorporating a liquid dielectric material between capacitor plates. In the latter examples, the liquid dielectric material may increase the effective maximum capacitance of the variable capacitor for a given capacitor plate geometry. The liquid dielectric material may further increase the electrical breakdown voltage of the capacitor for a given capacitor plate geometry. The liquid dielectric material may further provide for additional dissipation of thermal energy within the variable capacitor relative to, for example, a vacuum capacitor, owing to the potential of a liquid dielectric having a greater thermal conductivity than a vacuum.

FIG. 1 is a side external view of a vacuum variable capacitor 100 according to one or more examples. Vacuum variable capacitor 100 includes an enclosure 102 with an actuator end cap 104 as hereinafter described. In the example of FIG. 1 , enclosure 102 includes a first conductive collar 106 and a second conductive collar 108 electrically insulated from one another by an intermediate electrically insulating element 110 joined in a hermetic manner to conductive collars 106 and 108. In examples, conductive collars 106 and 108 may be a metal such as silver-plated copper, copper, brass, aluminum, or brazed aluminum. In examples, intermediate electrically insulating element 110 may be substantially cylindrical, and may be made of ceramic or another suitable insulating material.

An upper end of an actuator 114 extends out of actuator end cap 104. In some examples, actuator 114 may threaded, and may be rotated to advance and retract a movable capacitor assembly within enclosure 102. In other examples, actuator 114 may be advanced and retracted by means of a linear motor, an electromagnetic coil arrangement, or hydraulic or pneumatic systems. In examples, a first conductive mounting plate 116 may be provided in electrical contact with first conductive collar 106 to facilitate physical installation of vacuum variable capacitor 100 in operating environments. First conductive mounting plate 116 may further provide an external electrical connection to vacuum variable capacitor 100 as herein described. Vacuum variable capacitor 100 may further include a second conductive mounting plate 119 in electrical contact with conductive collar 108 to further facilitate installation of vacuum variable capacitor in operating environments.

FIG. 2 is a cut-away perspective view of vacuum variable capacitor 100 according to one or more examples. FIGS. 3 and 4 are a front cross-sectional views of vacuum variable capacitor 100. As illustrated in FIGS. 2-4 , contained within enclosure 102 are a first capacitor plate assembly 118 and a second capacitor plate assembly 120. First capacitor plate assembly 118 includes a first capacitor plate 122 coupled to a first electrode 124. First electrode 124 of first capacitor plate assembly 118 is coupled to the underside of a first mounting plate 126. Second capacitor plate assembly 120 includes a second capacitor plate 128 coupled to a second electrode 130. Second electrode of second capacitor plate assembly 120 is coupled to a bottom portion 132 of conductive collar 108.

FIG. 5 is an exploded perspective view of first capacitor plate assembly 118 and second capacitor plate assembly 120 according to one or more examples. As shown in FIG. 5 , first capacitor plate 122 and second capacitor plate 128 each comprise concentric cylindrical coil capacitor plates, with first capacitor plate 122 being electrically attached at a top end to first electrode 124 and configured as a cylindrical coil and second capacitor plate 128 attached at bottom end to second electrode 130 configured as a cylindrical coil. In this example, second capacitor plate varies in height from a maximum height at a central portion 140 of the capacitor plate coil to a minimum height at an outer portion 143 of the capacitor plate coil. (As used herein, the term “height” when describing a capacitor plate refers to the dimension of the capacitor plate extending away from a respective mounting plate.)

In examples, first and second capacitor plate assemblies 118 and 120 are configured such that first mounting plate 126 and bottom portion 132 of second collar 108 may be positioned relative to each other to enable first capacitor plate 122 to at least partially concentrically interdigitate with second capacitor plate 128. In examples, first capacitor plate 122 and second capacitor plate 128 do not contact each other directly, although the spacing between first mounting plate 126 and bottom portion 132 of second collar 108 may be adjusted, as described herein, to vary the length of concentric, overlapping interdigitation between first capacitor plate 122 and second capacitor plate 128, thereby adjusting the effective capacitance established between first capacitor plate 122 and second capacitor plate 128. In examples, first and second capacitor plates 122 and 128 may be made of materials (e.g., oxygen-free copper or copper-plated brass) conventionally used for such structures in a vacuum variable capacitor.

With continued reference to FIGS. 2-4 , and especially with references to FIGS. 3-4 , in one or more examples a flexible structure 134 is in sealed attachment between a top surface 136 of first mounting plate 126 and an inner top portion 138 of first collar 106. First electrode 124 is mechanically and electrically coupled to a bottom surface 142 of first mounting plate 126.

As shown in FIGS. 2-4 , actuator 114 extends through one or more gaskets 150 in actuator end cap 104 and through an aperture 152 in first collar 106, extending partially into flexible structure 134. In one or more examples, actuator 114 threadably engages a thrust assembly comprising a thrust collar 154 and an extended coupling 156 secured to first mounting plate 126.

With continued reference to FIGS. 2-4 , a plurality of separate volumes are defined within enclosure 102. In particular, with reference especially to FIGS. 3 and 4 , a first volume 158 is defined within actuator end cap 104 and within the interior of flexible structure 134. (Multiple reference numerals 158 appear in FIGS. 3 and 4 to indicate the extent of first volume 158).

A second volume 160 is defined within enclosure 102. (Again, multiple reference numerals 160 appear in FIGS. 3 and 4 to indicate the extent of second volume 160). As shown in FIGS. 3 and 4 . Second volume 160 is defined outside of flexible structure 134, within intermediate electrically insulating element 110, within second collar 108, between first and second capacitor plates 122 and 128.

In examples, first volume 158 may be at or near external, atmospheric pressure, due to a possibly nominal seal between actuator 114 and gaskets 150 as actuator enters actuator end cap 104. On the other hand, second volume 160 is hermetically (i.e., vacuum- and liquid-tight) sealed, due to sealed attachment of flexible structure 134 to first collar 106 and to first mounting plate 126, such as by brazing.

According to the present examples, the extent of interdigitated overlapping of first capacitor plate 122 and second capacitor plate 128, and hence the capacitive performance of vacuum variable capacitor, may be adjusted through rotation of actuator 114. Rotation of actuator 114, such as by a stepper motor or servo-motor (not shown) causes threads of actuator 114 to raise or lower thrust collar 154 and extended coupling 156, thereby raising or lowering first mounting plate 126 relative to second mounting plate 132. That is, in these examples, first mounting plate 126, carrying first capacitor plate assembly 118, is movable with respect to bottom portion 132 of second collar 108, carrying second capacitor plate assembly 120.

With reference specifically to FIGS. 3 and 4 , FIG. 3 shows vacuum variable capacitor 100 in a first operational configuration, in which thrust collar 154 and extended coupling 156 are advanced to a maximum extent into enclosure 102, such that the interdigitated overlap between first capacitor plate 122 and second capacitor plate 128 is at a maximum. This maximizes the capacitance between first capacitor plate 122 and second capacitor plate 128, due to the interdigitated overlap being at a maximum.

FIG. 4 shows vacuum variable capacitor 100 in a second operational configuration, in which thrust collar 154 and extended coupling 156 are retracted to a maximum extent from enclosure 102, such that the interdigitated overlap between first capacitor plate 122 and second capacitor plate 128 is at a minimum. This essentially minimizes the capacitance between first capacitor plate 122 and second capacitor plate 128 for this example, due to the interdigitated overlap being at a minimum. At points between full advancement and full retraction of thrust collar 154, and extended coupling 156, capacitance varies according to the overall interdigitated overlap of first capacitor plate 122 and second capacitor plate 128.

In examples, first mounting plate 126, flexible structure 134, extended coupling 156, thrust collar 154, and mounting plate 116 are conductive (e.g., metallic) and provide a low-resistance electrical conduction path between first electrode 124, first collar 106, and mounting plate 116, which may serve as a first external electrical contact for vacuum variable capacitor 100. Second electrode 130 is coupled to bottom portion 132 of second collar 108, and to bottom conductive plate 119 which may be integral with (or electrically coupled to) second collar 108, thereby enabling second collar 108 and bottom conductive plate 119 to serve as a second electrical connection to vacuum variable capacitor 100. To facilitate attachment of an electrode plate, a threaded socket 170 may be provided in second collar 108.

FIGS. 6 and 7 are a side, cross-sectional views of a vacuum variable capacitor 600 according to another example. In the example of FIGS. 6 and 7 , elements which are substantially identical to those of the example of FIGS. 2-5 are identified with the same reference numerals. One distinction of the example of FIGS. 6 and 7 is the geometry of a pair of capacitor plate assemblies 618 and 620 including concentrically interdigitated coiled capacitor plates 622 and 628. FIG. 8 is an exploded view of capacitor plate assemblies 618 and 620.

Like capacitor plate 128 in the example of FIG. 4 , capacitor plate 628 in the example of FIGS. 6-8 varies in height from a maximum height at a central coiled portion 640 to a minimum height at an outer portion 642. However, whereas capacitor plate 122 in the example of FIGS. 2-5 is a cylindrical coil of consistent height, in the example of FIGS. 6-8 , capacitor plate 622 in FIGS. 6-8 varies in height from a maximum height at a central coiled portion 644 to a minimum height at an outer coiled portion 646.

With reference specifically to FIGS. 6 and 7 , FIG. 6 shows vacuum variable capacitor 600 in a first operational configuration, in which thrust collar 154 and extended coupling 156 are advanced to a maximum extent into enclosure 102, such that the interdigitated overlap between first capacitor plate 622 and second capacitor plate 628 is at a maximum. This maximizes the capacitance between first capacitor plate 622 and second capacitor plate 628, due to the interdigitated overlap being at a maximum.

FIG. 7 shows vacuum variable capacitor 600 in a second operational configuration, in which thrust collar 154 and extended coupling 156 are retracted to a maximum extent from enclosure 102, such that the interdigitated overlap between first capacitor plate 622 and second capacitor plate 628 is at a minimum. This essentially minimizes the capacitance between first capacitor plate 622 and second capacitor plate 628 for this example, due to the interdigitated overlap being at a minimum. At points between full advancement and full retraction of thrust collar 154, and extended coupling 156, capacitance varies according to the overall interdigitated overlap of first capacitor plate 622 and second capacitor plate 628.

FIGS. 9 and 10 are a side, cross-sectional views of a vacuum variable capacitor 900 according to another example. In the example of FIGS. 9 and 10 , elements which are substantially identical to those of the example of FIGS. 2-5 are identified with the same reference numerals. The primary distinction of the example of FIGS. 9 and 10 is the geometry of a pair of capacitor plate assemblies 918 and 920 including concentrically interdigitated coiled capacitor plates 922 and 928. FIG. 11 is an exploded view of capacitor plate assemblies 918 and 920.

Like capacitor plate 128 in the example of FIG. 4 , capacitor plate 928 in the example of FIGS. 9-11 varies in height from a maximum height at a central coiled portion 940 to a minimum height at an outer portion 942. However, whereas capacitor plate 122 in the example of FIGS. 2-5 is a cylindrical coil of consistent height, in the example of FIGS. 9-11 , capacitor plate 922 in FIGS. 9-11 varies in height from a maximum height at a central coiled portion 944 to a minimum height at an outer coiled portion 946.

With reference specifically to FIGS. 9 and 10 , FIG. 9 shows vacuum variable capacitor 900 in a first operational configuration, in which thrust collar 154 and extended coupling 156 are advanced to a maximum extent into enclosure 102, such that the interdigitated overlap between first capacitor plate 922 and second capacitor plate 928 is at a maximum. This maximizes the capacitance between first capacitor plate 922 and second capacitor plate 928, due to the interdigitated overlap being at a maximum.

FIG. 10 shows vacuum variable capacitor 900 in a second operational configuration, in which thrust collar 154 and extended coupling 156 are retracted to a maximum extent from enclosure 102, such that the interdigitated overlap between first capacitor plate 922 and second capacitor plate 928 is at a minimum. This essentially minimizes the capacitance between first capacitor plate 922 and second capacitor plate 928 for this example, due to the interdigitated overlap being at a minimum. At points between full advancement and full retraction of thrust collar 154, and extended coupling 156, capacitance varies according to the overall interdigitated overlap of first capacitor plate 922 and second capacitor plate 928.

FIGS. 9 and 10 are a side, cross-sectional views of a vacuum variable capacitor 900 according to another example. In the example of FIGS. 9 and 10 , elements which are substantially identical to those of the example of FIGS. 2-5 are identified with the same reference numerals. The primary distinction of the example of FIGS. 9 and 10 is the geometry of a pair of capacitor plate assemblies 918 and 920 including concentrically interdigitated coiled capacitor plates 922 and 928. FIG. 11 is an exploded view of capacitor plate assemblies 918 and 920.

Like capacitor plate 128 in the example of FIG. 4 , capacitor plate 928 in the example of FIGS. 9-11 varies in height from a maximum height at a central coiled portion 940 to a minimum height at an outer portion 942. However, whereas capacitor plate 122 in the example of FIGS. 2-5 is a cylindrical coil of consistent height, in the example of FIGS. 9-11 , capacitor plate 922 in FIGS. 9-11 varies in height from a maximum height at a central coiled portion 944 to a minimum height at an outer coiled portion 946.

With reference specifically to FIGS. 9 and 10 , FIG. 9 shows vacuum variable capacitor 900 in a first operational configuration, in which thrust collar 154 and extended coupling 156 are advanced to a maximum extent into enclosure 102, such that the interdigitated overlap between first capacitor plate 922 and second capacitor plate 928 is at a maximum. This essentially maximizes the capacitance between first capacitor plate 922 and second capacitor plate 928, due to the interdigitated overlap being at a maximum.

FIG. 10 shows vacuum variable capacitor 900 in a second operational configuration, in which thrust collar 154 and extended coupling 156 are retracted to a maximum extent from enclosure 102, such that the interdigitated overlap between first capacitor plate 922 and second capacitor plate 928 is at a minimum. This essentially minimizes the capacitance between first capacitor plate 922 and second capacitor plate 928 for this example, due to the interdigitated overlap being at a minimum. At points between full advancement and full retraction of thrust collar 154, and extended coupling 156, capacitance varies according to the overall interdigitated overlap of first capacitor plate 922 and second capacitor plate 928.

FIGS. 12 and 13 are a side, cross-sectional views of a vacuum variable capacitor 900 according to another example. In the example of FIGS. 12 and 13 , elements which are substantially identical to those of the example of FIGS. 2-5 are identified with the same reference numerals. The primary distinction of the example of FIGS. 12 and 13 is the geometry of a pair of capacitor plate assemblies 1218 and 1220 including concentrically interdigitated coiled capacitor plates 922 and 928. FIG. 14 is an exploded view of capacitor plate assemblies 1218 and 1220.

In the example of FIGS. 12-14 , capacitor plates 1222 and 1228 each comprise coils that are generally conical in cross section where the height of the coil from a base is varied along its radius to achieve different performance results, the peaks of which being interdigitated with the other to varying extents depending upon the advancement or retraction of thrust collar 154 and extended coupling 156.

With reference specifically to FIGS. 12 and 13 , FIG. 12 shows vacuum variable capacitor 1200 in a first operational configuration, in which thrust collar 154 and extended coupling 156 are advanced to a maximum extent into enclosure 102, such that the interdigitated overlap between first capacitor plate 1222 and second capacitor plate 1228 is at a maximum. This maximizes the capacitance between first capacitor plate 1222 and second capacitor plate 1228, due to the interdigitated overlap being at a maximum.

FIG. 13 shows vacuum variable capacitor 1200 in a second operational configuration, in which thrust collar 154 and extended coupling 156 are retracted to a maximum extent from enclosure 102, such that the interdigitated overlap between first capacitor plate 1222 and second capacitor plate 1228 is at a minimum. This essentially minimizes the capacitance between first capacitor plate 1222 and second capacitor plate 1228 for this example, due to the interdigitated overlap being at a minimum. At points between full advancement and full retraction of thrust collar 154, and extended coupling 156, capacitance varies according to the overall interdigitated overlap of first capacitor plate 1222 and second capacitor plate 1228.

In the various examples herein, the geometries of the capacitor plates in the respective capacitor plate assemblies may achieve improved performance with respect to the variation in impedance of the capacitors across a range of variable capacitance. This, in turn, improves the tuning behavior of the variable capacitors, particularly when utilized in RF matching networks. Capacitors having capacitor plates of non-consistent height, as disclosed in various examples herein, and/or having profiles varying along a radius (such as the example of FIGS. 12-14 herein), may deviate from a linear function and begin to approximate a power function. That is, the change in impedance versus position of the variable capacitor plates may more closely approximate a linear function than a power function.

In examples, using a control algorithm for adjustment of the variable capacitance, a consistent tuning behavior may be achieved as the element being controlled has a more linear change in impedance as capacitance is varied. Furthermore, in various examples herein, where the heights of the capacitor plates is varied through the radius, the gap between capacitor plates can be varied along the radius in the same way, such that the effective voltage rating may increase as the variable capacitors are adjusted from maximum to minimum capacitance. This may increase the effective voltage of the variable capacitors in the various examples described herein, as the current rating is primarily a function of the real component of the load impedance, not the reactive component.

For example, FIG. 15 is a plot of the change in impedance as a function of capacitor plate displacement in a variable capacitor having two concentric, interdigitated cylindrical capacitor plates, such as described in the above-referenced concurrently filed and co-pending patent application S.N. XX/XXX,XXX. In FIG. 15 , a capacitance plot 1502 reflects the linear increase in capacitance as the displacement between capacitor plates in a variable capacitor having two concentric, interdigitated cylindrical plates is increased. At the same time, the change in impedance between the capacitor plates, reflected by curve 1504 in FIG. 15 exhibits a substantial variation, particularly in the interval identified with reference numeral 1506 in FIG. 15 . This substantial deviation in impedance over an operational interval may be undesirable, such as in radio-frequency (“RF”) matching network applications.

On the other hand, FIG. 16 is a plot of the change in impedance as a function of capacitor plate displacement in a variable capacitor having alternative capacitor plate geometries such as described herein with the examples of FIGS. 2-11 . In FIG. 16 , a capacitance plot.1602 reflects a non-linear (roughly 1/X) increase in capacitance as a function of capacitor plate displacement, due to the geometry of capacitor plates in the examples of FIGS. 2-11 . At the same time, the impedance differential, identified as curve 1604 in FIG. 16 , reflects less deviation overall between capacitance curve 1602.

Further, FIG. 17 is a plot of the change in impedance as a function of capacitor plate displacement for a capacitor as described herein with reference to FIGS. 12-14 . In FIG. 17 , a capacitance plot 1702 reflects a non-linear (roughly 1/X) increase in capacitance as a function of capacitor plate displacement, due to the geometry of capacitor plates in the examples of FIGS. 12-14 . At the same time, the impedance differential, identified as curve 1704 in FIG. 16 , reflects even less deviation overall between capacitance curve 1702.

One or more vacuum variable capacitors such as the vacuum variable capacitors from the examples of FIGS. 1-14 herein may be utilized for tuning and otherwise controlling matching networks in radio frequency plasma processing devices. RF plasma-enhanced processing is extensively used in semiconductor manufacturing to etch different types of films, deposit thin films at low to intermediate processing temperatures, and perform surface treatment and cleaning. One characteristic of such processes is the employment of a plasma, i.e., a partially ionized gas, that is used to generate neutral species and ions from precursors inside a reaction chamber, provide energy for ion bombardment, and/or perform other actions. Radio frequency plasma-enhanced processing is performed by what are known as radio frequency processing devices.

Radio frequency processing devices may include a radio frequency generator that transmits a signal to a plasma reaction chamber. A radio frequency matching device, which may have a variable impedance, may be located between the radio frequency generator and the plasma reaction chamber. The radio frequency matching device may be controlled, or otherwise tuned by varying the impedance of the radio frequency matching device. Tuning the radio frequency matching device reduces reflected power from the plasma reaction chamber and/or the radio frequency matching device, which may increase power that is transferred from the radio frequency generator to the plasma reaction chamber and into the plasma process. During operation, a radio frequency generator may be energized to form a plasma within a reaction chamber. The plasma may be produced after a source gas is injected into the reaction chamber and power is supplied within the reaction chamber by the radio frequency generator.

Under certain conditions, the power that is supplied to the reaction chamber may be reflected back from the reaction chamber. One cause of the reflected power may be a mismatch in the characteristic impedance of the system and the load formed by the plasma within the reaction chamber. To help prevent reflected power, a matching network may be disposed between the radio frequency generator and the reaction chamber. Such matching networks may include a number of variable capacitors or other impedance elements. The variable capacitors may be tuned so that the complex load impedance within the reaction chamber matches the impedance of the radio frequency generator.

While multiple methods of controlling or otherwise tuning matching networks have been used, such methods may not reliably and efficiently result in impedance matching. Matching networks may include stepper motors, which have a specific number of steps that are a function unique to a particular stepper motor. During operation, a capacitor may be driven by a motor that has a range between zero and one hundred percent and the motor may, as a result, have a number of clicks. Embodiments of the present disclosure may provide recipes and/or otherwise allow for the adjustment of a capacitor position based, at least in part, on “a steps to percent ratio.”

Turning to FIG. 18 , a schematic representation of a matching network including variable capacitors according to one or more examples is shown. In example of FIG. 18 , a matching network 1800 is illustrated having a matching branch 1802 and a splitter branch 1804. Matching branch 1802 receives radio frequency power from a radio-frequency (RF) input 1806. A first variable capacitor 1808 of the matching branch 1802 receives RF power from RF input 1806. First variable capacitor 1808 may be a variable capacitor such as that disclosed herein with reference to FIGS. 1-14 , and may be rated at approximately 10-2000 pF.

In the example of FIG. 18 , first variable capacitor 1808 is connected to a second capacitor 1810, which is connected to ground. Second capacitor 1810 is also connected to a third variable capacitor 1812. Third variable capacitor 1812 may also be a variable capacitor such as that disclosed herein with reference to FIGS. 1-14 and may be rated at approximately 10-2000 pF. Third variable capacitor 1812 is also connected to an inductor 1814, which further connects to splitter branch 1804.

Splitter branch 604 receives RF power from matching branch 1802, which, splits the received RF power between a fourth variable capacitor 1816 and a fifth variable capacitor 1818. Fourth variable capacitor 616 and fifth variable capacitor 1818 may also be variable capacitors such as that disclosed herein with reference to FIGS. 1-5 and may be rated at approximately 10-2000 pF.

Fifth variable capacitor 1818 is connected to an inner coil 1820. Between fifth variable capacitor 1818 and inner coil 1820, one or more sensors 1822 may be disposed. Sensor(s) 1822 may be used to measure, for example, voltage between fifth variable capacitor 1818 and ground. Similarly, fourth variable capacitor 1816 is connected to an outer coil 1824. Between fourth variable capacitor 1816 and outer coil 1824, one or more sensors 1826 may be disposed. Sensors 1826 may be used to measure, for example, voltage between fourth variable capacitor 1816 and ground.

Inner coil 1820 may further be connected to a ground and outer coil 1824 may be connected to circuitry that includes a sensor 1828 and a sixth capacitor 1830. Sensor 1828 may be used to measure, for example, voltage between outer coil 1824 and ground. Inner coil 1820 and outer coil 1824 may be located outside of the matching network 1800 circuitry, as indicated by dashed line 1832 in FIG. 18 .

The circuitry illustrated in FIG. 18 may be used to tune first variable capacitor 1808, third variable capacitor 1812, fourth variable capacitor 1816, and fifth variable capacitor 1818. By tuning first variable capacitor 1808, third variable capacitor 1812, fourth variable capacitor 1816, and fifth variable capacitor 1818, the power provided to inner coil 1820 and outer coil 1824 may be adjusted.

The circuitry, which in one embodiment may be employed in matching network 200 as a current split ratio matching network, may be controlled using a programmable logic controller (not shown), which may be disposed in or otherwise connected to matching network 1800.

The foregoing description, for purposes of explanation, uses specific nomenclature to provide a thorough understanding of the disclosure. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the systems and methods described herein. The foregoing descriptions of specific examples are presented for purposes of illustration and description. Examples herein are not intended to be exhaustive of or to limit this disclosure to the precise forms described. Many modifications and variations are possible in view of the above teachings. The examples are shown and described in order to best explain the principles of this disclosure and practical applications, to thereby enable others skilled in the art to best utilize this disclosure and various examples with various modifications as are suited to the particular use contemplated. It is intended that the scope of this disclosure be defined by the claims and their equivalents below. 

What is claimed is:
 1. A variable capacitor, comprising: an enclosure having an interior; a movable capacitor plate assembly disposed in the interior of the enclosure, the movable capacitor plate assembly including a first capacitor plate, a first electrode, and a first mounting plate; a flexible structure having a first end sealed around an opening into the interior of the enclosure and a second end sealed to a rear side of the first mounting plate; a fixed capacitor plate assembly disposed proximal to the first capacitor plate assembly, the fixed capacitor plate assembly including a second capacitor plate, a second electrode, and a second mounting plate; an actuator coupling assembly coupled to the rear side of the first mounting plate; an actuator having a longitudinal axis, extending into the opening and through the first flexible structure, a distal end of the actuator engaging with the actuator coupling assembly, the actuator for advancing and retracting the movable capacitor plate assembly with respect to the fixed capacitor plate assembly; wherein the first and second capacitor plates comprise interdigitated concentric cylindrical coils, the second capacitor plate having a greater height at a center portion of the capacitor plate coil and a lower height at an outer portion of the capacitor plate coil.
 2. The variable capacitor of claim 1, wherein the actuator includes threads for engaging the actuator coupling assembly, such that rotation of the actuator in a first direction advances the movable capacitor plate assembly toward the fixed capacitor plate assembly and expanding the flexible structure, and rotation of the threaded actuator in a second direction retracts the movable capacitor plate assembly away from the fixed capacitor plate assembly and contracting the flexible structure.
 3. The variable capacitor of claim 1, wherein flexible structure comprises a bellows structures.
 4. The variable capacitor of claim 1, wherein the first capacitor plate comprises a cylindrical coil having a constant height.
 5. The variable capacitor of claim 1, wherein the first capacitor plate comprises a cylindrical coil having a greater height at a center portion of the capacitor plate coil and a lower height at an outer portion of the capacitor plate coil.
 6. The variable capacitor of claim 4, wherein the advancing and retracting of the movable capacitor assembly varies the extent of overlapping interdigitation of the first and second capacitor plates, thereby varying the capacitance of the variable capacitor.
 7. The variable capacitor of claim 3, wherein enclosure includes a first conductive collar in electrical contact with the movable capacitor plate assembly, a second conductive collar in electrical contact with the fixed capacitor plate assembly, and an intermediate electrically insulating element separating the first conductive collar and the second conductive collar.
 8. The variable capacitor of claim 7, wherein the flexible structure provides a conductive connection between the movable capacitor plate assembly and the first conductive collar.
 9. The variable capacitor of claim 1, wherein a vacuum is maintained within the interior of the enclosure.
 10. The variable capacitor of claim 1, wherein a liquid dielectric is contained within the interior of the enclosure.
 11. A method of adjusting capacitance of a variable capacitor, comprising: providing an enclosure having an interior; providing a movable capacitor plate assembly disposed in the interior of the enclosure, the movable capacitor plate assembly including a first capacitor plate, a first electrode, and a first mounting plate; providing a flexible structure having a first end sealed around an opening into the interior of the enclosure and a second end sealed to a rear side of the first mounting plate; providing a fixed capacitor plate assembly disposed proximal to the first capacitor plate assembly, the fixed capacitor plate assembly including a second capacitor plate, a second electrode, and a second mounting plate; providing an actuator coupling assembly coupled to the rear side of the first mounting plate; providing an actuator having a longitudinal axis, extending into the opening and through the first flexible structure, a distal end of the actuator engaging with the actuator coupling assembly; and advancing and retracting the movable capacitor plate assembly with respect to the fixed capacitor plate assembly; wherein the first and second capacitor plates comprise interdigitated concentric cylindrical coils, the second capacitor plate having a greater height at a center portion of the capacitor plate coil and a lower height at an outer portion of the capacitor plate coil.
 12. The method of claim 11, wherein the actuator includes threads for engaging the actuator coupling assembly, such that rotation of the actuator in a first direction advances the movable capacitor plate assembly toward the fixed capacitor plate assembly and expanding the first flexible structure, and rotation of the threaded actuator in a second direction retracts the movable capacitor plate assembly away from the fixed capacitor plate assembly and contracting the first flexible structure.
 13. The method of claim 11, wherein the structure comprise a bellows structure.
 14. The method of claim 11, wherein the advancing and retracting of the movable capacitor assembly varies the extent of overlapping interdigitation of the first and second capacitor plates, thereby varying the capacitance of the variable capacitor.
 15. The method of claim 14, further comprising: providing a first conductive collar in electrical contact with the movable capacitor plate assembly, a second conductive collar in electrical contact with the fixed capacitor plate assembly, and an intermediate electrically insulating element separating the first conductive collar and the second conductive collar.
 16. The method of claim 15, wherein the first flexible structure provides a conductive connection between the movable capacitor plate assembly and the first conductive collar.
 17. The method of claim 11, further comprising: providing a liquid dielectric in the interior of the enclosure.
 18. The method of claim 11, further comprising: maintaining a vacuum in the interior of the enclosure.
 19. A variable capacitor, comprising: an enclosure having an interior; a movable capacitor plate assembly disposed in the interior of the enclosure, the movable capacitor plate assembly including a first capacitor plate, a first electrode, and a first mounting plate; a flexible structure having a first end sealed around an opening into the interior of the enclosure and a second end sealed to a rear side of the first mounting plate; a fixed capacitor plate assembly disposed proximal to the first capacitor plate assembly, the fixed capacitor plate assembly including a second capacitor plate, a second electrode, and a second mounting plate; an actuator coupling assembly coupled to the rear side of the first mounting plate; an actuator having a longitudinal axis, extending into the opening and through the first flexible structure, a distal end of the actuator engaging with the actuator coupling assembly, the actuator for advancing and retracting the movable capacitor plate assembly with respect to the fixed capacitor plate assembly; wherein the first and second capacitor plates each comprise coils having a conical cross section where the height of the first and second capacitor plate coils from a base is varied along its radius, the peaks of which being interdigitated to varying extents depending upon the advancement and retraction of the movable capacitor plate assembly.
 20. The variable capacitor of claim 19, wherein the actuator includes threads for engaging the actuator coupling assembly, such that such that rotation of the actuator in a first direction advances the movable capacitor plate assembly toward the fixed capacitor plate assembly and expanding the flexible structure, and rotation of the threaded actuator in a second direction retracts the movable capacitor plate assembly away from the fixed capacitor plate assembly and contracting the flexible structure.
 21. The variable capacitor of claim 19, wherein flexible structure comprises a bellows structure.
 22. The variable capacitor of claim 21, wherein the advancing and retracting of the movable capacitor assembly varies the extent of overlapping interdigitation of the first and second capacitor plates, thereby varying the capacitance of the variable capacitor.
 23. The variable capacitor of claim 19, wherein enclosure includes a first conductive collar in electrical contact with the movable capacitor plate assembly, a second conductive collar in electrical contact with the fixed capacitor plate assembly, and an intermediate electrically insulating element separating the first conductive collar and the second conductive collar.
 24. The variable capacitor of claim 23, wherein the flexible structure provides a conductive connection between the movable capacitor plate assembly and the first conductive collar.
 25. The variable capacitor of claim 19, wherein a vacuum is maintained within the interior of the enclosure.
 26. The variable capacitor of claim 19, wherein a liquid dielectric is contained within the interior of the enclosure. 